Dear All,
as we have to cast the Geopolymer concrete insitu at sea island, if sea water to be used can we add 5% OPC to accelerate curing in ambient temperature. The fly ash with 1.5% CaO and we add 5% OPC ( equal to 3% CaO) the total CaO wt% is still within the limit of low C Fly ash. Perhaps we treat sea water first with OPC and let MgSO4 to react instantly with CaOH inside the OPC that would reduce the reactant lime inside the concrete. I tried it and found it set very fast and cured well but suspicious about future strength of the concrete anyhow.
thank you for your sharing.
with my best regards.
Pham van Hung
10% OPC was found to be the optimum for early and final strength based on (Lateef et al, 2016)
Hello Hung,
in my opinion you still continue to realize alkali activated materials, real geopolymer product doesn't need OPC to accelerate setting, there are several way to accelerate setting time and hardening using minerals , or reducing liquid/binder ratio with superplasticizers but in my experience OPC produces hydrates so final structure will be not a geopolymer but maybe a good AAF. If you want to avoid collateral effects as cracks, corrosion, or efflorescence you have to think how do better binder that can set at room temperature using also sea water, so I suggest to avoid OPC and use other raw materials, like slag but take care to dosage to reduce at minimum free CaO to avoid corrosion and secondary reactions.
Please to use the correct terminology, there are already too much confusion yet about geopolymer technology, is necessary that experts use correct terminology.
Alkali activated materials are different from geopolymer about materials involved, chemistry and liquids used, the only comparison is about liquids but in geopolymers I use a pH of 13,3 very close to pH of OPC (you can put your finger inside without corrosive effects=user friendly), not very high pH (low NaOH at maximum, that is user hostile) that produces efflorescence and destruction of fly ash instead of depolymerization... I hope to be useful for your topic, because if you use OPC you doesn't satisfy the first target of Geopolymer technology so reduce pollution of CO2 ,due to clincker production .
Correct me if I am not adequately answering your question directly.
First off, we need to know the contents of the sea water, as it is essentially a heterogeneous ionic solution with much impurities. The use of sea water itself have an effect on the geopolymerisation reaction. Whether sea water is acidic or not also depends on where it was obtained (Near the clean beach? Near factories discharging substances? Near a wastewater treatment plant effluent?).
Curing is accelerated with increased temperature, although there may be many other factors like pH or addition of other substances (nanomaterial, OPC powder, etc.). Therefore, I suggest studying each component separately before arriving at any conclusions.
Hopefully my statements will provide useful insights for you.
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